The invention relates to a cover and counterbalancing mechanism, and more particularly to a platen cover for a copying machine containing a sheet transport and alignment mechanism and having a compound counterbalancing system.
Typical prior art is exemplified by Taylor et al U.S. Pat. No. 4,135,805 which teaches the utility of a gas spring and a tension spring acting in opposition to counterbalance a platen cover that raises past the vertical. The tension spring is arranged to increasingly counter the force exerted by the gas spring as the cover is moved from the closed to the open position. This compensates for the reduced force exerted by the platen cover as it is opened. In the open position, the cover has moved past the vertical, and the tension spring is effective to counter the force exerted by the cover between vertical and the open position. All material copied is exposed through the platen. A transport mechanism in the cover moves the material across the platen.
Caldwell U.S. Pat. No. 4,043,665 teaches the utility of a spring assist counterbalance for a platen cover which contains a transport mechanism. The transport mechanism moves the material being copied across the exposure platen. The counterbalance spring provides operator assistance in the manual lifting of the cover unit up away from the platen into a raised or upright position and for retaining the entire unit in that upright position.
Menon et al U.S. Pat. No. 3,997,265 teaches the use of a coil spring cooperating with a counterbalance weight. The weight neutralizes the weight of the cover and the spring urges the cover to the open position so that the machine operator may readily raise the cover.
Halvorsen et al U.S. Pat. No. 3,642,376 teaches the use of torsional springs to urge the platen cover apparatus in an upward position until engaging a stop at approximately 70.degree. to the horizontal. When the platen cover apparatus is to be closed on a document or book positioned on the platen glass, a downward force must be exerted against the action of the spring members until a latch member engages a locking member on the machine frame, releasably actuatable by a solenoid.
Knechtel U.S. Pat. No. 4,110,030 teaches machine structure for copying both sides of single sheet documents and for the copying of pages of bound volumes. A separate platen is used for exposing the bound volumes, and a traveling scanning system is used. Single sheets are scanned as they are moved past an exposure window located on the axis of a drum. The sheets traverse a diameter of the drum during exposure. The drum is then rotated through 180 degrees and the sheet motion reversed to copy the second side of the sheet.
Suzuki et al U.S. Pat. No. 4,158,497 teaches copying machine structure having a large platen and a moving optical system for copying bound volume material. The bound volume original remains stationary and is illuminated by a slit illuminating device which is reciprocated. For copying single sheets, the original is moved and a slit illuminating device remains stationary. Provision is made for making different size copies from the size of the original by varying the optical path lengths and the rates of movement.